TheHardware/SowareInterface · UniversityofWashington* QuickAnnouncements*! Website:...

University of Washington

The Hardware/So7ware Interface CSE351 Summer 2013

Instructor: Benjamin Wood Teaching Assistants: Jacob Gile, Riley Klingler

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Course Staff

Winter 2013 IntroducCon 2

Ben instructor

Jacob TA

Riley TA


Who are you? ¢  22ish students

¢  Majors, non-‐majors

¢  Fans of computer science, no doubt!

¢  Who has wriRen a program: §  in Java? §  in C? §  in Assembly language? §  with mulGple threads?

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Quick Announcements ¢  Website: cs.uw.edu/351 ¢  SecCon locaCon to be updated soon… ¢  Lab 0 released, due Friday 5pm.

§  Simple exercises to get familiar with C. §  Credit/no-‐credit.

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The Hardware/So7ware Interface ¢  What is hardware? So7ware?

¢  What is an interface?

¢  Why do we need a hardware/so7ware interface?

¢  Why do we need to understand both sides of this interface?

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C/Java, assembly, and machine code

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if (x != 0) y = (y+z)/x;!

cmpl $0, -4(%ebp) je .L2 movl -12(%ebp), %eax movl -8(%ebp), %edx leal (%edx, %eax), %eax movl %eax, %edx sarl $31, %edx idivl -4(%ebp) movl %eax, -8(%ebp) .L2:

1000001101111100001001000001110000000000 0111010000011000 10001011010001000010010000010100 10001011010001100010010100010100 100011010000010000000010 1000100111000010 110000011111101000011111 11110111011111000010010000011100 10001001010001000010010000011000


C/Java, assembly, and machine code

l  The three program fragments are equivalent l  You'd rather write C! -‐ a more human-‐friendly language l  The hardware likes bit strings! -‐ everything is voltages

l  The machine instrucGons are actually much shorter than the number of bits we would need to represent the characters in the assembly language

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if (x != 0) y = (y+z)/x;!

cmpl $0, -4(%ebp) je .L2 movl -12(%ebp), %eax movl -8(%ebp), %edx leal (%edx, %eax), %eax movl %eax, %edx sarl $31, %edx idivl -4(%ebp) movl %eax, -8(%ebp) .L2:

1000001101111100001001000001110000000000 0111010000011000 10001011010001000010010000010100 10001011010001100010010100010100 100011010000010000000010 1000100111000010 110000011111101000011111 11110111011111000010010000011100 10001001010001000010010000011000

ê

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HW/SW Interface: The Historical PerspecCve ¢  Hardware started out quite primiCve

§  Hardware designs were expensive ⇒ instrucGons had to be very simple – e.g., a single instrucGon for adding two integers

¢  So7ware was also very basic §  SoQware primiGves reflected the hardware preSy closely

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Hardware

Architecture Specification (Interface)


HW/SW Interface: Assemblers ¢  Life was made a lot beRer by assemblers

§  1 assembly instrucGon = 1 machine instrucGon, but... §  different syntax: assembly instrucGons are character strings, not bit

strings, a lot easier to read/write by humans §  can use symbolic names

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Hardware User

program in

asm

Assembler specification

Assembler


HW/SW Interface: Higher-‐Level Languages ¢  Higher level of abstracCon:

§  1 line of a high-‐level language is compiled into many (someGmes very many) lines of assembly language

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Hardware User

program in C

C language specification

Assembler C compiler


HW/SW Interface: Code / Compile / Run Times

Hardware User

program in C

Assembler C compiler

Code Time Compile Time Run Time

Note: The compiler and assembler are just programs, developed using this same process.

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.exe file .c file


Outline for today ¢  Course themes: big and liRle ¢  Roadmap of course topics ¢  Three important realiCes ¢  How the course fits into the CSE curriculum ¢  LogisCcs

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The Big Theme: Interfaces and AbstracCons ¢  CompuCng is about abstracCons

§  (but we can’t forget reality) ¢  What are the abstracCons that we use? ¢  What do YOU need to know about them?

§  When do they break down and you have to peek under the hood? §  What bugs can they cause and how do you find them?

¢  How does the hardware (0s and 1s, processor execuCng instrucCons) relate to the so7ware (C/Java programs)? §  Become a beSer programmer and begin to understand the important

concepts that have evolved in building ever more complex computer systems

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Roadmap

car *c = malloc(sizeof(car)); c->miles = 100; c->gals = 17; float mpg = get_mpg(c); free(c);

Car c = new Car(); c.setMiles(100); c.setGals(17); float mpg = c.getMPG();

get_mpg: pushq %rbp movq %rsp, %rbp ... popq %rbp ret

Java: C:

Assembly language:

Machine code:

0111010000011000 100011010000010000000010 1000100111000010 110000011111101000011111

Computer system:

OS:

Memory, data, & addressing Integers & floats Machine code & C x86 assembly Procedures & stacks Arrays & structs Memory & caches Processes Virtual memory Memory allocaCon Java vs. C

Roadmap


LiRle Theme 1: RepresentaCon ¢  All digital systems represent everything as 0s and 1s

§  The 0 and 1 are really two different voltage ranges in the wires ¢  “Everything” includes:

§  Numbers – integers and floaGng point §  Characters – the building blocks of strings §  InstrucGons – the direcGves to the CPU that make up a program §  Pointers – addresses of data objects stored away in memory

¢  These encodings are stored throughout a computer system §  In registers, caches, memories, disks, etc.

¢  They all need addresses §  A way to find them §  Find a new place to put a new item §  Reclaim the place in memory when data no longer needed

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LiRle Theme 2: TranslaCon ¢  There is a big gap between how we think about programs and

data and the 0s and 1s of computers ¢  Need languages to describe what we mean ¢  Languages need to be translated one step at a Cme

§  Words, phrases and grammars

¢  We know Java as a programming language §  Have to work our way down to the 0s and 1s of computers §  Try not to lose anything in translaGon! §  We’ll encounter Java byte-‐codes, C language, assembly language, and

machine code (for the X86 family of CPU architectures)

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LiRle Theme 3: Control Flow ¢  How do computers orchestrate the many things they are

doing? ¢  In one program:

§  How do we implement if/else, loops, switches? §  What do we have to keep track of when we call a procedure, and then

another, and then another, and so on? §  How do we know what to do upon “return”?

¢  Across programs and operaCng systems: §  MulGple user programs §  OperaGng system has to orchestrate them all

§  Each gets a share of compuGng cycles §  They may need to share system resources (memory, I/O, disks)

§  Yielding and taking control of the processor §  Voluntary or “by force”?

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Course Outcomes ¢  FoundaCon: basics of high-‐level programming (Java) ¢  Understanding of some of the abstracCons that exist

between programs and the hardware they run on, why they exist, and how they build upon each other

¢  Knowledge of some of the details of underlying implementaCons

¢  Become more effecCve programmers §  More efficient at finding and eliminaGng bugs §  Understand some of the many factors that influence program

performance §  Facility with a couple more of the many languages that we use to

describe programs and data

¢  Prepare for later classes in CSE

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Reality #1: ints ≠ integers & floats ≠ reals ¢  RepresentaCons are finite ¢  Example 1: Is x2 ≥ 0?

§  Floats: Yes! §  Ints:

§  40000 * 40000 -‐-‐> 1600000000 §  50000 * 50000 -‐-‐> ??

¢  Example 2: Is (x + y) + z = x + (y + z)? §  Unsigned & Signed Ints: Yes! §  Floats:

§  (1e20 + -‐1e20) + 3.14 -‐-‐> 3.14 §  1e20 + (-‐1e20 + 3.14) -‐-‐> ??

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Reality #2: Assembly sCll maRers ¢  Why? Because we want you to suffer?

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Reality #2: Assembly sCll maRers ¢  Chances are, you’ll never write a program in assembly code

§  Compilers are much beSer and more paGent than you are

¢  But: understanding assembly is the key to the machine-‐level execuCon model §  Behavior of programs in presence of bugs

§  High-‐level language model breaks down §  Tuning program performance

§  Understand opGmizaGons done/not done by the compiler §  Understanding sources of program inefficiency

§  ImplemenGng system soQware §  OperaGng systems must manage process state

§  FighGng malicious soQware §  Using special units (Gmers, I/O co-‐processors, etc.) inside processor!

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Assembly Code Example ¢  Time Stamp Counter

§  Special 64-‐bit register in Intel-‐compaGble machines §  Incremented every clock cycle §  Read with rdtsc instrucGon

¢  ApplicaCon §  Measure Gme (in clock cycles) required by procedure

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double t; start_counter(); P(); t = get_counter(); printf("P required %f clock cycles\n", t);


Code to Read Counter ¢  Write small amount of assembly code using GCC’s asm facility ¢  Inserts assembly code into machine code generated by

compiler

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/* Set *hi and *lo (two 32-bit values) to the high and low order bits of the cycle counter. */ void access_counter(unsigned *hi, unsigned *lo) { asm("rdtsc; movl %%edx,%0; movl %%eax,%1"

: "=r" (*hi), "=r" (*lo) /* output */ : /* input */ : "%edx", "%eax"); /* clobbered */

}


Reality #3: Memory MaRers ¢  So, what is memory?

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Reality #3: Memory MaRers ¢  Memory is not unbounded

§  It must be allocated and managed §  Many applicaGons are memory-‐dominated

¢  Memory referencing bugs are especially pernicious §  Effects are distant in both Gme and space

¢  Memory performance is not uniform §  Cache and virtual memory effects can greatly affect program

performance §  AdapGng program to characterisGcs of memory system can lead to

major speed improvements

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Memory Referencing Bug Example

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double fun(int i) { volatile double d[1] = {3.14}; volatile long int a[2]; a[i] = 1073741824; /* Possibly out of bounds */ return d[0]; }

fun(0) –> 3.14 fun(1) –> 3.14 fun(2) –> 3.1399998664856 fun(3) –> 2.00000061035156 fun(4) –> 3.14, then segmentation fault


Memory Referencing Bug Example

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double fun(int i) { volatile double d[1] = {3.14}; volatile long int a[2]; a[i] = 1073741824; /* Possibly out of bounds */ return d[0]; }

fun(0) –> 3.14 fun(1) –> 3.14 fun(2) –> 3.1399998664856 fun(3) –> 2.00000061035156 fun(4) –> 3.14, then segmentation fault

Saved State

d7 … d4

d3 … d0

a[1]

a[0] 0

1

2

3

4

LocaCon accessed by fun(i)

ExplanaCon:


Memory Referencing Errors ¢  C (and C++) do not provide any memory protecCon

§  Out of bounds array references §  Invalid pointer values §  Abuses of malloc/free

¢  Can lead to nasty bugs §  Whether or not bug has any effect depends on system and compiler §  AcGon at a distance

§  Corrupted object logically unrelated to one being accessed §  Effect of bug may be first observed long aQer it is generated

¢  How can I deal with this? §  Program in Java (or C#, or ML, or Haskell, or Ruby, or Racket, or …) §  Understand what possible interacGons may occur §  Use or develop tools to detect referencing errors

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Memory System Performance Example ¢  Hierarchical memory organizaCon ¢  Performance depends on access paRerns

§  Including how program steps through mulG-‐dimensional array

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void copyji(int src[2048][2048], int dst[2048][2048]) { int i,j; for (j = 0; j < 2048; j++) for (i = 0; i < 2048; i++) dst[i][j] = src[i][j]; }

void copyij(int src[2048][2048], int dst[2048][2048]) { int i,j; for (i = 0; i < 2048; i++) for (j = 0; j < 2048; j++) dst[i][j] = src[i][j]; }

21 Cmes slower (PenCum 4)


CSE351’s role in the CSE Curriculum ¢  Pre-‐requisites

§  142 and 143: Intro Programming I and II §  Also recommended: 390A: System and SoQware Tools

¢  One of 6 core courses §  311: FoundaGons of CompuGng I §  312: FoundaGons of CompuGng II §  331: SW Design and ImplementaGon §  332: Data AbstracGons §  351: HW/SW Interface §  352: HW Design and ImplementaGon

¢  351 provides the context for many follow-‐on courses.

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CSE351’s place in the CSE Curriculum

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CSE351

CSE451 Op Systems

CSE401 Compilers

Concurrency

CSE333 Systems Prog

Performance

CSE484 Security

CSE466 Emb Systems

CS 143 Intro Prog II

CSE352 HW Design

Comp. Arch.

CSE461 Networks

Machine Code

Distributed Systems

CSE477/481/490/etc. Capstone and Project Courses

The HW/SW Interface: underlying principles linking hardware and so3ware

ExecuCon Model

Real-‐Time Control


Course PerspecCve ¢  This course will make you a beRer programmer.

§  Purpose is to show how soQware really works §  By understanding the underlying system, one can be more effecGve as a

programmer. §  BeSer debugging §  BeSer basis for evaluaGng performance §  How mulGple acGviGes work in concert (e.g., OS and user programs)

§  Not just a course for dedicated hackers §  What every CSE major needs to know §  Job interviewers love to ask quesGons from 351!

§  Provide a context in which to place the other CSE courses you’ll take

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Textbooks ¢  Computer Systems: A Programmer’s PerspecCve, 2nd EdiCon

§  Randal E. Bryant and David R. O’Hallaron §  PrenGce-‐Hall, 2010 §  hSp://csapp.cs.cmu.edu §  This book really maSers for the course!

§  How to solve labs §  PracGce problems typical of exam problems

¢  A good C book – any will do §  The C Programming Language (Kernighan and Ritchie) §  C: A Reference Manual (Harbison and Steele)

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Course Components ¢  Lectures (25)

§  Introduce the concepts; supplemented by textbook

¢  SecCons (8+) §  Applied concepts, important tools and skills for labs, clarificaGon of

lectures, exam review and preparaGon

¢  WriRen homework assignments (4) §  Mostly problems from text to solidify understanding

¢  Labs (5, plus “lab 0”) §  Provide in-‐depth understanding (via pracGce) of an aspect of system

¢  Exams (midterm + final) §  Test your understanding of concepts and principles §  Midterm currently scheduled for Wednesday, July 24, in class. §  Final is definitely Friday, August 23, in class (last day).

¢  Summer quarter is only 9 weeks long! 34


Resources ¢  Course web page

§  cs.uw.edu/351 §  Schedule, policies, labs, homeworks, and everything else

¢  Course discussion board §  Keep in touch outside of class – help each other §  Staff will monitor and contribute

¢  Course mailing list – check your @uw.edu §  Low traffic – mostly announcements; you are already subscribed

¢  Office hours, appointments, drop-‐ins §  Poll: will be posted this week

¢  Staff e-‐mail: cse351-‐[email protected] §  Things that are not appropriate for discussion board or beSer offline

¢  Anonymous feedback §  Any comments about anything related to the course where you would

feel beSer not aSaching your name 35


Policies: Grading ¢  Exams (35%): 15% midterm, 20% final ¢  WriRen assignments (20%): weighted according to effort

§  We’ll try to make these about the same

¢  Lab assignments (45%): weighted according to effort §  These will likely increase in weight as the quarter progresses

¢  Late days: §  3 late days to use as you wish throughout the quarter – see website

¢  CollaboraCon: §  hSp://www.cs.washington.edu/educaGon/courses/cse351/13su/

policies.html §  hSp://www.cs.washington.edu/students/policies/misconduct

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Other details ¢  Consider taking CSE 390A, 1 credit, useful skills ¢  Poll: office hours + reschedule secCon 2 (week of July 4)

§  (OH) Monday late morning / aQernoon §  (OH, S2) Tuesday late morning / aQernoon §  (OH, S2) Wednesday late morning / aQernoon §  (OH) Thursday late morning / aQernoon §  (OH, S2) Friday late morning / aQernoon

¢  Lab 0 due Friday 5pm. §  On the website §  Non-‐majors accounts §  CSE home VM §  Thursday secGon on C and tools.

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Welcome to CSE351! ¢  Let’s have fun ¢  Let’s learn – together ¢  Let’s communicate ¢  Let’s make this a useful class for all of us ¢  Many thanks to the many instructors who have shared their

lecture notes – I will be borrowing liberally through the qtr – they deserve all the credit, the errors are all mine §  CMU: Randy Bryant, David O’Halloran, Gregory Kesden, Markus Püschel §  Harvard: MaS Welsh (now at Google-‐SeaSle) §  UW:

Gaetano Borriello, Hal Perkins, John Zahorjan, Peter Hornyack, Luis Ceze

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